The present invention relates generally to a stereo camera system for obtaining a stereo image of an object to measure distance between the stereo camera system and the object using those, and more particularly, to the stereo camera system constructed to obtain the stereo image by a camera. The present invention also relates to a distance measurement system and a distance measurement method for measuring distance between the stereo camera system and an object using disparity of a stereo image of the object.
Disparity of a stereo image on a computer vision can be used in measuring distance between an object and a camera that obtains the stereo image by photographing the object. Disparity means distance between two homologous points on two images of an object, that is, distance between a point on a first image of a pair of stereo images and a corresponding point on a second image of the stereo images.
A conventional stereo camera system 40 used in distance measurement consists of two charge coupled device cameras (CCD camera) 41 and 42 as showed in FIG. 8. The stereo image shown in FIG. 9 is obtained as follows; one of the stereo images is obtained by photographing an object using a first camera 41, and the other is obtained by photographing the object using a second camera 42. A point 43 on the object corresponds to both a first homologous point 47 on a first image 45 and a second homologous point 48 on a second image 46. The distance between the point 43 of the object and a stereo camera system 40 is in a functional relationship with the disparity of the stereo image, that is, the distance between the first homologous point 47 and the second homologous point 48. Still, the focal length and other intrinsic parameters of each camera 41 or 42 can affect the distance between the point 43 of the object and the stereo camera system 40. Furthermore, differences between intensities of the first image 45 and the second image 46 owing to a small range of variation in the irises of the first and second cameras 41 and 42 results in not only taking much time to detect the homologous points 47 and 48 but also deteriorating reliability of such detection. Meanwhile, the method for obtaining the first image 45 by exposure using the first camera 41, and then obtaining the second image 46 by another exposure using the second camera 42 can not be applied in the dynamic situation if the object and/or the stereo camera system 40 is moved.
In consideration of the above defects of the stereo camera system, there were proposed some kinds of stereo camera systems to obtain a stereo image using only a camera, as follows.
In a paper of Y. Nishimoto and Y. Shirai which is entitled xe2x80x9cA feature-based stereo model using small disparitiesxe2x80x9d and published in Proceedings in Computer Vision and Pattern Recognition, pp. 192-196, 1987, a stereo camera system as shown in FIG. 10 is proposed. The stereo camera system 50 comprises a camera 51 and a rotary glass plate 52 arranged at a desirable distance from the front side of the lens of the camera 51. The rotary glass plate 52 swings between a first rotated position represented by a solid line and a second rotated position represented by a dotted line. As the glass plate 52 swings between the first rotated position and the second rotated position when the stereo camera system 50 is fixed, the optical axis of the lens of the camera 51 is moved slightly. A stereo image is obtained as follows. One of the stereo images is obtained by photographing an object by an exposure using the camera 51 with the glass plate 52 positioned at the first rotated position, and the other stereo image is obtained by photographing the object by another exposure using the camera 51 with the glass plate 52 positioned at the second rotated position. Since the range of disparity of the stereo image obtained by the stereo camera system 50 is very narrow, it is difficult to measure distance between the object and the stereo camera system 50 precisely. Furthermore, the stereo camera system 50 can not be applied in a dynamic situation due to the two different exposure times as is the in the aforementioned stereo camera system 40.
In a paper of W. Teoh and X. D. Zhang which is entitled xe2x80x9cAn inexpensive stereoscopic vision system for robots,xe2x80x9d published in Int. Conf. Robotics, pp. 186-189, 1984, another stereo camera system as shown in FIG. 11 is proposed. The stereo camera system 60 comprises a camera 61, a rotary glass plate 62 arranged at a desirable distance from the front side of the lens of the camera 61 and two fixed glass plates 63 and 64 disposed at both sides of the rotary glass plate 62. The stereo camera system 60 operates as the aforementioned stereo camera system 50 does except that range of disparity of the stereo image obtained by the stereo camera system 60 is broader than that by the stereo camera system 50. Accordingly, the stereo camera system 60 can not be applied at a dynamic situation due to the two different exposure times as in the aforementioned stereo camera system 40.
In a paper of A. Goshtasby and W. A. Gruver entitled xe2x80x9cDesign of a Single-Lens Stereo camera systemxe2x80x9d and published in Pattern Recognition, vol. 26, pp. 923-936, 1993, still another stereo camera system, as shown in FIG. 12, is proposed. The stereo camera system 70 comprises a camera 71 and two reflectors 72 and 73 disposed in two planes crossed with each other so that the two reflectors 72 and 73 abut against each other at their sides. The two reflectors 72 and 73 are oppositely inclined so that their specular surfaces obliquely face an object. The camera 71 is disposed to simultaneously photograph two images reflected by the specular surfaces of the two reflectors 72 and 73. Since the stereo camera system 70 photographs reflected images, that is, reversed images, any picture obtained by the stereo camera system 70 is object to an image translation process. Brightness of each image of the picture is affected by an incidence angle of a prevailing source of light to each reflector 72 or 73 because of mutual reflection between the two reflectors 72 and 73, whereby degrees of brightness of two images in the picture are different although they are obtained at a single exposure time.
Therefore, the present invention is aimed to make a stereo camera system for providing a frame of picture having a stereo image of an object to be constructed by only a camera.
The present invention is also aimed to provide the stereo camera system for providing a frame of picture having a stereo image by a single exposure in a dynamic situation while all images of the picture have an equivalent brightness.
In order to accomplish the above mentioned aims, this invention provides a stereo camera system for providing a frame of picture having a stereo image of an object used in distance measurement between the stereo camera system and the object. The stereo camera system comprises a camera and a prism arranged at a desirable distance from the front side of the lens of the camera.
The prism may comprise a delta shaped biprism having a base, a first incline and a second incline, in which the first incline and the second incline obliquely face the lens of the camera.
The prism may comprise a triagonal pyramid shaped triprism having a base and three inclines, in which the three inclines obliquely face the lens of the camera.
The invention also provides a system for measuring distance between a stereo camera system and an object using disparity of a stereo image of the object obtained by the stereo camera system and the object, in which the stereo camera system comprises a camera and a prism arranged at a desirable distance from the front side of the lens of the camera. The distance measurement system comprises means for obtaining a frame of picture comprising the stereo image by a single shot using said stereo camera system; means for detecting homologous points on the stereo image, in which the homologous points correspond to a point on the object; means for measuring distance between the homologous point; and means for calculating the distance between said stereo camera system and the object from the distance between the homologous point.
If the prism of said stereo camera system comprises a delta shaped biprism having a base, a first incline and a second incline, in which the first incline and the second incline obliquely face the lens of the camera, there are provided stereo images of the object by the means for obtaining a frame of picture.
If the prism of said stereo camera system comprises a triagonal pyramid shaped triprism having a base and three inclines, in which the three inclines obliquely face the lens of said camera, there are provided triple images of the object are obtained by the means for obtaining a frame of picture.
The invention also provides a distance measurement method for measuring distance between a stereo camera system and an object using disparity of a stereo image of the object obtained by the stereo camera system and the object. The method comprises steps for providing the stereo camera system comprising a camera and a prism arranged at a desirable distance from the front side of the lens of said camera; obtaining a frame of picture comprising the stereo image by a single shot using said stereo camera system; detecting homologous points on the stereo image, in which the homologous points correspond to a point on the object; measuring distance between the homologous point; and calculating the distance between said stereo camera system and the object from the distance between the homologous point.
The method may further comprise steps for obtaining information in relation to distance between the stereo camera system and each of plural points on the object by repeating the steps for detecting homologous points, measuring distance between the homologous point and calculating the distance between said stereo camera system and the object; calculating magnification between life-size and imaginal size of the object; and calculating three dimensional size of the object from the information in relation to distance between the stereo camera system and each of plural points on the object, and the magnification between life-size and imaginal size of the object.
Other advantages and features of the present invention will become apparent from the following description, including the drawings and claims.